Polycystic kidney disease (PKD) encompasses a variety of kidney cystic disorders characterized by abnormal growth and development of renal cysts. Currently, there is no treatment for this disease, and the cost of management of PKD patients with end stage renal disease in the US exceeds $500 million annually. One of the most promising areas for therapy involves dietary intervention. In order to develop nutritional strategies for effective PKD management, however, the molecular defects underlying this disease need to be elucidated. The hypothesis of this proposal is that renal phosphatidylinositol (PtdIns) 3-kinase, PtdIns 4-kinase, phospholipase A2 (PLA2), and phospholipase Cgamma1 (PLCgamma1) are altered in kidneys from pcy mice, an animal model of PKD, compared to kidneys of normal mice. Furthermore, it is hypothesized that the delayed progression of PKD noted in response to dietary protein restriction is associated with the attenuation of abnormalities in these phosphoinositide-related enzymes. These hypotheses are based on data showing that renal phosphoinositide metabolism is altered in the pcy mouse and that reducing dietary protein to a low, but adequate level, is effective in retarding the progression of PKD in pcy mice. Therefore, specific aim 1 is to determine the protein levels, and either mRNA levels or enzyme activities of PtdIns 3-kinase, PtdIns 4-kinase, PLA2 and PLCgamma1 in kidneys and livers of mice with PKD compared to normal mice. Specific aim 2 is to determine the effect of a low protein diet on these phosphoinositide-related enzymes. To address these specific aims, kidneys and livers from normal and diseased (pcy) male mice at an early (60 d) and a late (180 d) stage of the disease will be analyzed. Using immunoblotting, the steady state levels of renal PtdIns 3-kinase, PtdIns 4-kinase, PLA2, and PLCgamma1 will be determined. If these are altered, the mRNA levels will be determined by ribonuclease protection assays. If the steady state levels of these enzymes are not altered, however, the activity of these enzymes will be determined by immunoprecipitation and in vitro enzyme activity assays. These studies will determine whether the steady state levels, and mRNA or activity levels of these select enzymes are altered in pcy kidneys. In the second part of this proposal, normal and pcy animals will be fed normal and low protein diets to investigate the effect of protein restriction on these phosphoinositide-related enzymes. Understanding the molecular mechanisms by which dietary protein restriction elicits its beneficial effect will further the development of treatments for PKD. Any therapy that even slows the progression of this disease will have significant impact.